将 CGPathRef 转换为 NSBezierPath

Question

在 Apple 文档中，他们为您提供了如何将 NSBezierPath 转换为 CGPathRef 的代码。我需要反过来转换，从 CGPathRef 到 NSBezierPath。 UIBezierPath 有一个名为 cgPath 的属性，所以如果我在 iPhone 上工作，那不会有问题，但我在 MacOS 上工作。

这一定是个老问题了，我肯定能在网上找到答案，但运气不好。可能是我遗漏了什么。任何帮助表示赞赏。

Answer 1

老问题，但我相信这对其他人仍然有帮助。（您没有指定 Objective-C 或 Swift；这是一个 Objective-C 答案。）

您可以使用 CGPathApply() 将 CGPathRef 转换为 NSBezierPath，并使用应用函数回调将 CGPathRef 点转换为 NSBezierPath 点。唯一棘手的部分是从 CGPathRef 的二次曲线到 NSBezierPath 的三次曲线的转换，但是 there's an equation for that:

Any quadratic spline can be expressed as a cubic (where the cubic term is zero). The end points of the cubic will be the same as the quadratic's.
 CP0 = QP0
 CP3 = QP2 
The two control points for the cubic are:
 CP1 = QP0 + 2/3 * (QP1-QP0)
 CP2 = QP2 + 2/3 * (QP1-QP2)
... There is a slight error introduced due to rounding, but it is usually not noticeable.

使用上面的等式，这里有一个 NSBezierPath 类别，用于从 CGPathRef:

转换

NSBezierPath+BezierPathWithCGPath.h

@interface NSBezierPath (BezierPathWithCGPath)
+ (NSBezierPath *)JNS_bezierPathWithCGPath:(CGPathRef)cgPath; //prefixed as Apple may add bezierPathWithCGPath: method someday
@end

NSBezierPath+BezierPathWithCGPath.m

static void CGPathToBezierPathApplierFunction(void *info, const CGPathElement *element) {
    NSBezierPath *bezierPath = (__bridge NSBezierPath *)info;
    CGPoint *points = element->points;
    switch(element->type) {
        case kCGPathElementMoveToPoint: [bezierPath moveToPoint:points[0]]; break;
        case kCGPathElementAddLineToPoint: [bezierPath lineToPoint:points[0]]; break;
        case kCGPathElementAddQuadCurveToPoint: {
            NSPoint qp0 = bezierPath.currentPoint, qp1 = points[0], qp2 = points[1], cp1, cp2;
            CGFloat m = (2.0 / 3.0);
            cp1.x = (qp0.x + ((qp1.x - qp0.x) * m));
            cp1.y = (qp0.y + ((qp1.y - qp0.y) * m));
            cp2.x = (qp2.x + ((qp1.x - qp2.x) * m));
            cp2.y = (qp2.y + ((qp1.y - qp2.y) * m));
            [bezierPath curveToPoint:qp2 controlPoint1:cp1 controlPoint2:cp2];
            break;
        }
        case kCGPathElementAddCurveToPoint: [bezierPath curveToPoint:points[2] controlPoint1:points[0] controlPoint2:points[1]]; break;
        case kCGPathElementCloseSubpath: [bezierPath closePath]; break;
    }
}

@implementation NSBezierPath (BezierPathWithCGPath)
+ (NSBezierPath *)JNS_bezierPathWithCGPath:(CGPathRef)cgPath {
    NSBezierPath *bezierPath = [NSBezierPath bezierPath];
    CGPathApply(cgPath, (__bridge void *)bezierPath, CGPathToBezierPathApplierFunction);
    return bezierPath;
}
@end

这样调用：

//...get cgPath (CGPathRef) from somewhere
NSBezierPath *bezierPath = [NSBezierPath JNS_bezierPathWithCGPath:cgPath];

将 CGPathRef 转换为 NSBezierPath

Convert CGPathRef to NSBezierPath

macos

nsbezierpath

cgpathref